Separating apparatus

ABSTRACT

Apparatus for separating a mixture of materials into two categories such as potatoes and stones comprises a source of radiation such as X rays through which the mixture is passed, and detecting means responsive differently to the incidence of the radiation on the two categories of material. Directing means such as deflecting fingers, cause the material of the two different categories to be directed in different directions in response to the said different responses of the detecting means. The detecting means are responsive to the incidence of the radiation on material of both categories, and there are provided means for deriving from the detecting means a monitoring signal representative of responses by the detecting means arising from both categories of material. Visual indicator means may display the said monitoring signal, to give a measure representative of the projected area of the mixture, which passes through the radiation in given time. Alternatively or in addition there may be included control means for varying the supply of mixture to the separating means in dependence upon the monitoring signal.

Unite States Palmer atent 1191 Primary Exanziner-Harold A. Dixon SEPARATING APPARATUS [75] Inventor: John Palmer, Midlothian, Scotland Agent or Flmi cushman Darby &

[73] Assignee: National Research Development Corporation, London, England [57] ABSTRACT [22] Filed: 131 1973 Apparatus for separating a mixture of materials into 2 App]. 350 9 3 two categories such as potatoes and stones comprises a source of radiation such as X rays through which the mixture is passed, and detecting means responsive dif- [30] Forelgn fl f f ffi f ferently t0 the incidence of the radiation on the two P 1972 United Kingdom -18l27/72 categories of material. Directing means such as defleeting fingers. cause the material of the two different Cl 09/11 1.5, 250/ 3, categories to be directed in different directions in re- 250/367 sponse to the said different responses of the detecting [51] int. Cl H01] 39/12, 606m 7/00 means, The detecting means are responsive to the inl l Field 05 Search 209/1115, cidence of the radiation on material of both catego- 2 /3 367 ries, and there are provided means for deriving from the detecting means a monitoring signal representative [561 References Cited of responses by the detecting means arising from both UNlTED STATES PATENTS categories of material. Visual indicator means may 2,158,069 5/1939 Grover 250/223 display theFaid monitorifig Signal, give a mfiasure 2.433560 12/1947 Hurley 250/223 representaflve Of the Projected area of the mlxture, 3 137 392 6/1964 Slight 4 209/1115 which passes through the radiation in given time. Al- 3 225963 l2/l965 Arpajian 250/223 ternatively or in addition there may be included con- 3.594\57 97 Ga t A 209/1115 trol means for varying the supply of mixture to the Slight v t v t l eparating means in dependence upon the monitoring signal. I

11 Claims, 3 Drawing Figures CONTROL uiNlT 34' F PULSE T I/IIRI [SWNG comm/a ith 5, REFERENCE MEANS Ni/INS COW? COUNT 1 J J i I i COMPARATOR 34 I1 i i /?FRNC 22 I N I LEVEL 2(7) 30 r 2 I GENERATOR SESE l H/iU/IU/O/V i OUfU/NG 7' 33 sou/1a; 1 ozv/crs 24 L [HER GENERATOR I r-'' /o /E" i EE i SECOND SIGNAL- 3/ @ZM Pom r055 omrcm/s com /mm LEVEL ANALYSER REFERENCE firv/crs 11 i LEvEL GENERATOR FIRST SIGNAL-LEVEL/I ANALYSER MEANS I MEANS l 1 SEPARATING APPARATUS The present invention relates to apparatusfor separating a mixture of materials into two categories of materials, and is concerned in particular, but not exclusively, with apparatus for harvesting root crops, for example potatoes, and for separating the crops from stones, earth and the like.

In our U.S Pat. Nos. 3,137,392 and 3,209,910, there is disclosed apparatus for separating potatoes from other material such as stones, earth and the like, in which a mixture of potatoes and the other material is fed between a source of ionising radiation and an array of detecting devices which are able to distinguish between the presence of a potato in the region ofa detecting device and the presence of other material. The outputs of the detecting devices are fed to an array of defleeting devices to which the mixture is passed after passing through the beam of radiation, and the deflecting devices are arranged to deflect potatoes and other material respectively in different directions in dependence upon the response of the corresponding detecting devices to the presence or absence of potatoes. The mixture of potatoes and other material is conveniently fed to the separating apparatus by conveying means.

According to the present invention there-is provided apparatus for separating a mixture of materials into two categories of materials, comprising a source of radiation through which the mixture is arranged to pass, detecting means responsive both to the incidence of the radiation on material of a first category and to the incidence of the radiation on material of a second category, but responsive differently to the incidence of the radiation on the two categories of material, directing means for causing the material of the two different categories to be directed in different directions in response to the said different responses of the detecting means, and means for deriving from the detecting means a monitoring signal representative of responses by the detecting means arising from both categories of material.

The source of radiation may comprise means for providing a beam or array of beams spread laterally across the path of the mixture which is arranged to be passed through the beam in a corresponding laterally spread formation, the said detecting means and directing means having an efficiency in separating the categories of materials which is related to the projected area of the mixture, projected in a plane normal to the radiation, which passes through the radiation in a given time, and there may be provided visual indicator means for displaying the said monitoring signal, the said monitoring signal being arranged to give a measure representative of the said projected area of the mixture which passes through the radiation in a given'time.

Alternatively or in addition there may be included conveyor means for conveying the mixture in a relatively uniform layer for passage through the radiation in the laterally spread formation, and control means for varying the supply of mixture by the conveyor means in dependence upon the monitoring signal in such a manner as to tend to maintain the said projected area at a predetermined value.

The said conveyor means may comprise a conveyor belt, and the said means for varying the supply of the mixture may comprise means for varying the rate of supply of the mixture to the conveyor belt while maintaining the speed of the conveyor belt constant.

The conveyor belt may conveniently by arranged to convey. the mixture over an end roller of the conveyor belt, the mixture being arranged to pass through the radiation by falling past the source of radiation to the directing means.

The invention finds particular application where the said mixture comprises a mixture of a crop, (such as potatoes) and stones and other unwanted material. The apparatus may be mounted on a mobile frame for movement over the ground from which the crop is to be harvested, and may include means for harvesting the crop and means for varying the rate at which the crop is harvested and passed through the radiation, whereby the supply of the mixture can be varied in response to a comparison of the monitoring signal with a predetermined value thereof corresponding to an optimum efficiency of separation of the mixture.

Thus the monitoring signal may be compared with a reference signal to generate a difference signal, and the ground speed of the apparatus may be increased or decreased according to the sense and magnitude of the difference signal.

The variation of ground speed may be utilised for example to take account of variations in the amount of crop harvested per unit length travelled by the machine.

In a preferred arrangement, the source of radiation comprises means for providing a series of periodic pulses of ionising radiation, and the mixture of materials is arranged to pass between the'source and the detecting means. The said detecting means then comprises an array of discrete detecting devices each of which detects the attenuation of a pulse of radiation from the source when that pulse has been attenuated by the mixture, and the means for deriving the monitoring signal comprises means for measuring the rate of occurrence of responses due to attenuated pulses from the discrete devices to give a measure representative of the projected area of the mixture, projected normal to the radiation, which passes through the radiation in a given time.

Where, for example, the apparatus is adapted to separate potatoes from stones and other unwanted materials, the said directing means may comprise a plurality of fingers upon which the mixture is arranged to fall after passing through the radiation, each finger being controlled by a corresponding detecting device aligned with the finger in relation to the path of fall of the material each detecting device being arranged to differentiate between a potato and unwanted material as the mixture passes that detecting device, and the corre sponding finger being actuated to direct thepotato or unwanted material in the appropriate direction under the control of the associated detecting device.

Embodiments of the present invention will now be described by way of example, with reference to the accompanying drawings in which:

F IG. 1 is a general view of the main parts of a harvesting and separating apparatus;

FIG. 2 is a detail view ofa detecting device'of the apparatus of FIG. 1, and I FIG. 3 is a block diagram of such an apparatus when embodying the present invention.

The invention finds use with the potato separators described in our U.S. Pat. Nos. 3,137,392 and 3,209,910 a general description of such a separator will now be given. It is to be appreciated however, that the present invention finds application in other separators for example apparatus for separating coal from unwanted material, and is not limited to the kind of separator disclosed in British Patent Specifications Nos. 984232 and 1004222.

Referring now to FIG. 1, a belt conveyor 11 delivers a mixture 12 of harvested potatoes, stones, soil clods, to a vertical chute 13 formed in a housing not shown. This chute terminates at its lower end in an array of defleeting devices 14 which constitute directingmeans. The deflectingdevices consist of an array of movable fingers 15 extending across the width of and defining the bottom of the chute 13. In its upper position, each finger 15 is inclined at about 40 to the horizontal and presents a sloping surface leading towards a second conveyor 16.

Referring to FIG. 2, each movable finger 15 is pivotally mounted adjacent its upper end, and is held in the upper position shown by a pair of piston and cylinder devices 17 controlled by an electropneumatic valve acting as a switch 18. Operation of the switch 18 moves the finger 15 to its lower position shown in broken lines.

Referring again to FIG. 1, at the top of the chute 13 an array of detecting .devices 19 constitutes detecting means responsive to interruption of beams 20 of ionising radiation directed on to the detecting devices 19, by a source 21 of ionising radiation located in a housing on the other side of the chute 13. Each of the detecting devices 19 corresponds to a finger l5. Potatoes and stones passing down the chute 13 and through the radiation beams 20 cause the intensity of radiation received by each detecting device 19 to vary. This variation in intensity is used by each intensity detecting device 19 to energise its associated switch 18 if the degree of absorption of radiation is greater than a predetermined amount. Thus if a stone interrupts the beam to one detecting device, the intensity signal from that device is used to energise the corresponding switch 18 after elapse of a predetermined time interval just less than the time for the stone to fall to the corresponding finger 15', for example 90 milliseconds. As a result, when the stone reaches the corresponding finger 15, the finger is in its lower position and the stone falls freely. After the stone has passed, the finger returns to its upper position at the end of a futher predetermined time interval. On the other hand, when a potato passes through the beam 20, the intensity detected is somewhat greater, and the switch 18 is not energised. Therefore the finger 15 remains in its upper position so as to deflect the potato towards the discharge conveyor 16.

The beams of ionising radiation 34 are obtained from a small x-ray tube, although any other suitable source could be utilised, such as an isotope emitting gamma radiation. The radiation is pulse modulated, so that each detector 19 indicates the presence of an object by a series of output pulses of reduced intensity, the degree of intensity reduction indicating the nature of the object, and the number of reduced pulses indicating the size of the object in one dimension. A steel shield houses the x-ray tube and permits radiation therefrom to pass through a horizontal flare 22 in the side of the detection chute 13 to impinge on the horizontally disposed bank of intensity detectors 1 9.

Each intensity detecting device 19 may use a luminophor, for example calcium tungstate, in association with a photosensitive device, for example a photoelectron multiplier. The luminophor produces light proportional in intensity to the intensity of the'radiation striking it and the pulses of light are converted into electrical impulses by the photo-electron multiplier. The assembly of detecting devices 19 is provided with a steel housing 23, the rays 20 passing through a window of synthetic plastics material.

In FIG. 3 there is shown in diagrammatic form the function of the electronic circuits in one embodiment of the invention. The means for carrying out these functions by electronic circuits will be known. to one skilled in the art and will not be described in detail. It will be appreciated that other circuit arrangements may be used in other embodiments, for exampleat some stages digital circuits may be replaced by analogue cit cuits. Referring to FIG. 3 there will firstly be described,

the use of outputs of the detecting devices 19 in a known separating apparatus. The output signals of the plurality of detecting devices 19 are fed one to each of a corresponding plurality of comparator circuits of which one is shown at 24. In the comparator 24 the level of each output pulse from the associated detector 19 is compared with a reference level from a reference circuit 25 individual to that-comparator 24. The refer? ence signal is set to discriminate between the radiation absorption due to a potato, and that due to a stone. Each comparator 24 is set to produce an output pulse if and only if the radiation detected by the associated detecting device 19 falls below a first threshold value corresponding to an absorption produced by a stone, clod or the like. In a preferred arrangement, the output of each comparator 24 is fed not only to its associated deflecting device 14, but also to the one or more adjacent defiecting devices 14. Thus, two ormore fingers may be moved under the control of a response by one detecting device. The detection of a potato produces a fall in output signal of the device 19 insufficient to trigger the associated comparator 24. The output of each comparator 24 is fed to its associated deflecting device 14, and the occurrence of large absorption moves one or a number of deflecting devices to lower positions to allow the stone which has been detected to fall through the bottom of the chute 13.

Thus, in effect, when a stone passes down the chute 13, the beam 20 to one or more intensity detectors 19 is attenuated, the corresponding switches 18 are operated, and the stone passes through to be discharged. When a potato passes down the chute 13, the beams are not attenuated sufficiently to operate the switches, and the potato strikes the fingers and rolls down the incline into the delivery chute.

There will now be described the utilization of the present invention in the machine hereinbefore described.

The remainder of the circuits shown in FIG. 3- are concerned with means for deriving, in accordance with the present invention, a monitoring signal 26 which gives a measure of the throughput of the machine in a form which can be related to the degree of efficiency of separation of potatoes from stones and the like. It is desirable to optimise the throughput of a potato harvester by increasing the rate of harvesting until the effi ciency of separating the potatoes from unwanted material begins to fall to an uneconomic degree. It is one object of the present invention to provide a measurable parameter of the throughput of the machine in a form that gives a practical criterion of the optimum running of the machine.

In the embodiment illustrated, the parameter chosen is the projected area of the mixture of stones and potatoes which attenuates the radiation by an amount corresponding to either a stone or a potato. This level of attenuation is a level less than that set by the comparator 24 in FIG. 3, which corresponds to an attenuation by a stone.

The present invention can be understood more clearly by considering firstly the current methods of use of known potato harvesters incorporating x-ray separators.

Observation of these machines in the hands of users leads to the conclusion that users rarely load the separator correctly and usually underload it. Ideally the machine operator should have selected an appropriate tractor gear and adjusted his forward speed to maintain a constant quantity of material on the presentation belt,

irrespective of variations in the number and size of potatoes, stones and clods present in the dug material at that part of the field. In practice the operator cannot see the presentation belt and even if he were able to do so, he would need much skill and concentration not only to accomodate for variation but also to maintain a constant standard. The driver of a tractor drawing the harvester not only controls the forward speed but must steer the machine down the drill. Other aspects of the machines performance too must be monitored and thus the amount of time that can be actually spent attending to the presentation belt is limited. As it is impossible for the driver to see the presentation belt he relies on his examination of the rejected material for wrongly sorted potatoes to know whether he is going too fast. Observation suggests the belt is usually run in practice at 60-70 percent of its capacity. The belt seldom, if ever, reaches 100 percent loading. Some of the time it is likely to be running at about 50 percent of its capacity.

For the purposes of throughput control a harvester with x-ray separator consists essentially of a digging or harvesting mechanism, conveyors driven by the power take-off shaft of the towing tractor, a presentation belt driven at constant speed, and an x-ray separator mechanism. Throughput is determined primarily by the quantity of potatoes, stones and clods lifted per unit length of potato drill multiplied by the forward speed of the towing tractor. Usually, changes in forward speed produce immediate proportional changes in throughput at the share and on p.t.o. driven conveyors, but the presentation belt of the x-ray separator (which is independently driven, for example at a constant speed of 1% ft/s) introduces a delay of approximately 4 seconds between the time of change in forward speed and the time of change in throughput at the x-ray sepathe monitoring signal, the forward speed of the har vester is varied to tend to maintain the monitoring signal at the optimum value. Variations from the valti e will typically be caused by variations in crop, type (if;

In some circumstances the latter method may be preferable, as it may be desirable to maintain the engine speed of the tractor constant (to maintain p.t.o. speeds constant) and to vary the ground speed of the harvester by changing gears on the tractor.

In the present embodiment, the criterion selected is the projected area of the mixture to be separated, projected in a plane normal to the radiation through which the mixture passes. The following description with reference to FIG. 3 is concerned with one way of deriving such a monitoring signal.

Referring to FIG. 3, the output of eachdetecting device 19, in addition to being fed to a comparator 24 individual thereto, is also fed to a further comparator 27 individual thereto. Only one such comparator 27 is shown in the figure. Each comparator 27 compares the output pulse of the detecting device 19 with a further referencesignal from a reference circuit 28, and provides an output pulse for each radiation pulse received by the associated detecting device 19 which is attenuated by an amount corresponding to either a stone or a potato. The output pulses of the comparator 27, and of all the other comparators 27 corresponding to the array of detecting devices 19, are then fed to a counter 29. The counter 29 is thus set to count any radiation pulse of reduced intensity due to the detection of any object by a detecting device, whether a potato or object of other material. A timer 30 triggers the counter 29 to count for a predetermined interval and to give an output signal indicating the count at the end of the interval. This count does not usually give a count of the number of objects passing the detecting devices 19, as one object may span two or more devices, but it does give a measure of the projected area of the mixture. The output of the counter 29 may thus constitute a monitoring signal, and may be fed directly to an indicator 31 to indicate to the driver of the harvesting means whether the throughput is at the optimum value.

Alternatively, or in addition, the output of the counter 29 may be fed to a comparator 32 which compares the count with a reference count from a reference circuit 33 and produces an error signal proportional to the difference. The output of the comparator 32 is fed to a control unit 34' on the harvesting means 34 for varying the ground speed of the harvesting machine, in a sense such as to tend to restore the count to the reference level. By way of example the control unit may comprise a stepper motor controlled by the output of the comparator 32 and arranged to alter a linkage to the engine governor.

As an alternative (not shown) to the timer 30 and counter 29, the pulses representing responses of the detector devices 19 may be summed in an analogue integrator such as a capacitor charged by the pulses and discharged at a fixed rate, the error signal being provided by comparison of the voltage across the capacitor with a reference voltage.

As has been mentioned a harvester throughput is directly related to tractor speed which in turn depends on the setting of the tractor governor for a given gear. Automatic control of throughput can conveniently be achieved by means for setting the governor while allowing the tractor operator to be able to over-ride the setting if he judges it necessary. I

The governor setting actuator (not shown) can consist of a controlled stepper motor which drives the governor bell crank to the required-position by means of a worm and wheel reduction and a slip clutch. Thus the tractor operators speed control lever can be arranged to move according to the stepper motors commands, and if held by the operator the commands can be nullified by slipping the friction clutch.

One practical method of utilising the monitoring signal derived in accordance with the invention makes use of a rule of thumb criterion for a potato harvester that the projected area of material on the presentation belt, projected in the plane of the belt, should be roughly 80 percent of the belt area. The presentation belt normally travels at a constant speed which is set so that the trajectory of the mixture passing over the end roller of the belt intersects the radiation and deflecting fingers at appropriate positions. Material heaped on the input end of the belt from a previous elevator is spread into a single layer by a pair of contra-reciprocating finger combs (shown at 35 in FIG. 1) which deposit the objects from the. top layers into spaces in the bottom layer. A suitable throughput is generally obtained when the material deposited on the presentation belt can be spread into a continuous single layer each object just touching its neighbours. Too much material leads to double layering and hence sorting errors; too little and the separator is not loaded to its capacity.

As has been mentioned the supply of material to the separator can be controlled by altering the forward speed of the prime mover attached to the machine. This slows or speeds the intake of material and at the same time changes all the machine conveyor speeds apart from the presentation belt which is independently driven.

Thus the steps which may be followed in setting up a harvester may include:

i. setting an optimum speed of the presentation belt for the required trajectory;

ii. determining by observation a value of monitoring signal equivalent to an 80 percent projected area of material on the presentation belt; and

iii. varying the tractor speed in operation to keep the monitoring signal at the selected value.

I claim:

1. Apparatus for separating a mixture of bodies of a conveyor belt for passing said mixture of bodies in a laterally spread formation between the radiation source and said array of detecting devices; first signal-level analyzer means adapted to analyze v the output signal levels of said detecting devices for distinguishing bodies of one category from bodies of another category in dependence upon the degree of attenuation of said ionizing radiation by the different materials of the bodies;

an array of deflecting devices adapted to pass bodies of different materials in different directions under the control of said first analyzer means; and

second signal-level analyzer means connected to the outputs of said detecting devices for producing a throughput monitoring signal by combining the signal responses of said detecting devices resulting from attenuation of radiation by all bodies in the mixture, the output of said second analyzer means being connected to said control means to control said rate of supply of the mixture in dependence upon said throughput monitoring signal.

2. Apparatus for separating a mixture of bodies of different materials into at least two categories of materials, comprising:

means for supplying a mixture of bodies of different material at a variable rate of supply;

control means for controlling the rate of supply of said mixture;

a source of ionizing radiation arranged to produce a laterally spread beam or array of beams of radiation;

an array of radiation detecting devices positioned to receive radiation from said source;

conveyor belt-means for passing said mixture of bodies in axlaterally spread formation between said radiationsource and said array of detecting devices;

first signal-lever analyzer means adapted to analyze the output signal levels of said detecting devices for distinguishing bodies of one category from bodies of another category in dependence upon the degree of attenuation of said ionizing radiation by the different materials of the bodies;

an array of deflecting devices adapted to pass bodies of different materials in different directions under the control of said first analyzer means; and

second signal-level analyzer means connected to the outputs of said detecting devices for producing a throughput monitoring signal by combining the signal responses of said detecting devices resulting from attenuation of radiation by all bodies in the mixture;

and indicator means connected to the output of said second signal-level analyzer means and adapted to indicate the value of said throughput monitoring signal.

3. Apparatus for separating an agricultural crop from stones, clods and other unwanted material, comprising: harvesting means for harvesting the crop at a variable rate of harvesting;

I control means for controlling the rate of harvesting of said harvesting means; a source of ionizing radiation arranged to produce a laterally spread beam or arrayof beams of radiation; an array of radiation detecting devices positioned to receive radiation from the said source;

conveyor belt means for passing said crop and unwanted material in a laterally spread formation between said radiation source and said array of detecting devices;

first signal-level analyzer means adapted to analyze the output signal levels of said detecting devices for distinguishing the crop from the unwanted material in dependence upon the degree of attenuation of said ionizing radiation by the crop and the unwanted material;

an array of deflecting devices adapted to pass the crop and the unwanted material in different directions under the control of said first analyzer means;

second signal-level analyzer means connected to the outputs of said detecting devices for producing a throughput monitoring signal by combining the signal responses of said detecting devices resulting from attenuation of radiation by both crop and unwanted material;

and indicator means connected to the output of said second signal-level analyzer means for indicating the value of said throughput monitoring signal.

4. Apparatus according to claim 3 wherein said conveyor belt means is arranged to convey said crop and unwanted material over an end roller of said conveyor 1 belt means, and said conveyor belt means is so positioned that said crop and unwanted material passing over said end roller falls between said radiation source and said array of detecting devices.

5. Apparatus according to claim 3 wherein said source of ionizing radiation generates periodic pulses of radiation and said detecting devices provide output signals in the form of pulses corresponding to the pulses of radiation received, and said second signal-level analyzer means includes counter means arranged to sum all output pulses from said detecting devices which have diminished magnitudes due to radiation attenuation.

6. Apparatus for separating an agricultural crop from stones, clods and other unwanted material, comprising:

harvesting means for harvesting the crop at a variable rate of harvesting;

control means for controlling the rate of harvesting of said harvesting means;

a source of ionizing radiation arranged to produce a laterally spread beam or array of beams of radiation;

an array of radiation detectingdevices positioned to receive radiation from said source;

conveyor belt means for passing said crop and unwanted material in a laterally spread formation between said radiation source and said array of detecting devices;

first signal-level analyzer means adapted to analyze the output signal levels of said detecting devices for distinguishing the crop from the unwanted material in dependence upon the degree of attenuation of said ionizing radiation by the crop and the unwanted material; an array of deflecting devices adapted to pass the crop and the unwanted material in different directions under the control of said first analyzer-means; 5 and second signal-level analyzer means connected to the outputs of said detecting devices for'producing a throughput monitoring signal by combining the signal responses of saiddetecting devices resulting from attenuation of radiation by both crop and unwanted material, the output of said second analyzer means being connected to said control means of said harvesting means to control the rate of harvesting in dependence upon said throughput monitoring signal. 7. Apparatus according to claim 6 wherein said conveyor belt means is arranged to convey said crop and unwanted material over an end roller of said conveyor belt means, and said conveyor belt means is so positioned that said crop and unwanted material passing over said end roller falls between said radiation source and said array of detecting devices.

8. Apparatus according to claim 7 wherein said defleeting devices comprise a plurality of fingers upon which said crop and unwanted material fall after passing through said radiation, each finger being controlled by at least one corresponding detecting device aligned with said finger in relation to the'path of fall of said crop and unwanted material, each detecting device being arranged to differentiate between the crop and unwanted material as the mixture passes that detecting device, and said corresponding finger being actuated to pass the crop or unwanted material in the appropriate direction under the control of said associated detecting device or devices.

9. Apparatus according to claim 6 wherein said source of ionizing radiation generates periodic pulses of radiation and said detecting devices provide output signals in the form of pulses corresponding to the pulses of radiation received, and said second signal-level analyzer means includes counter means arranged to sum all output pulses from said detecting devices which have diminished magnitudes due to radiation attenuation.

10. Apparatus according to claim 9 in which said second signal-level analyzer means includes a reference generator means for generating a reference count corresponding to an optimum harvesting rate, and a reference comparator connected to compare said reference count with the output of said counter means, the output of said reference comparator being connected to feed a difference signal to said control means whereby the 7 rate of harvesting is increased or decreased according to the sense and magnitude of the difference signal.

11. Apparatus according to claim 6 wherein said control means comprises means for varying the ground speed of said harvesting means. 

1. Apparatus for separating a mixture of bodies of different materials into at least two categories of materials, comprising: means for supplying a mixture of bodies of different materials at a variable rate of supply; control means for controlling the rate of supply of the said mixture; a source of ionizing radiation arranged to produce a laterally spread beam or array of beams of radiation; an array of radiation detecting devices positioned to receive radiation from said course; a conveyor belt for passing said mixture of bodies in a laterally spread formation between the radiation source and said array of detecting devices; first signal-level analyzer means adapted to analyze the output signal levels of said detecting devices for distinguishing bodies of one category from bodies of another category in dependence upon the degree of attenuation of said ionizing radiation by the different materials of the bodies; an array of deflecting devices adapted to pass bodies of different materials in different directions under the control of said first analyzer means; and second signal-level analyzer means connected to the outputs of said detecting devices for producing a throughput monitoring signal by combining the signal responses of said detecting devices resulting from attenuation of radiation by all bodies in the mixture, the output of said second analyzer means being connected to said control means to control said rate of supply of the mixture in dependence upon said throughput monitoring signal.
 2. Apparatus for separating a mixture of bodies of different materials into at least two categories of materials, comprising: means for supplying a mixture of bodies of different material at a variable rate of supply; control means for controlling the rate of supply of said mixture; a source of ionizing radiation arranged to produce a laterally spread beam or array of beams of radiation; an array of radiation detecting devices positioned to receive radiation from said source; conveyor belt means for passing said mixture of bodies in a laterally spread formation between said radiation source and said array of detecting devices; first signal-lever analyzer means adapted to analyze the output signal levels of said detecting devices for distinguishing bodies of one category from bodies of another category in dependence upon the degree of attenuation of said ionizing radiation by the different materials of the bodies; an array of deflecting devices adapted to pass bodies of different materials in different directions under the control of said first analyzer means; and second signal-level analyzer means connected to the outputs of said detecting devices for producing a throughput monitoring signal by combining the signal responses of said detecting devices resulting from attenuatioN of radiation by all bodies in the mixture; and indicator means connected to the output of said second signal-level analyzer means and adapted to indicate the value of said throughput monitoring signal.
 3. Apparatus for separating an agricultural crop from stones, clods and other unwanted material, comprising: harvesting means for harvesting the crop at a variable rate of harvesting; control means for controlling the rate of harvesting of said harvesting means; a source of ionizing radiation arranged to produce a laterally spread beam or array of beams of radiation; an array of radiation detecting devices positioned to receive radiation from the said source; conveyor belt means for passing said crop and unwanted material in a laterally spread formation between said radiation source and said array of detecting devices; first signal-level analyzer means adapted to analyze the output signal levels of said detecting devices for distinguishing the crop from the unwanted material in dependence upon the degree of attenuation of said ionizing radiation by the crop and the unwanted material; an array of deflecting devices adapted to pass the crop and the unwanted material in different directions under the control of said first analyzer means; second signal-level analyzer means connected to the outputs of said detecting devices for producing a throughput monitoring signal by combining the signal responses of said detecting devices resulting from attenuation of radiation by both crop and unwanted material; and indicator means connected to the output of said second signal-level analyzer means for indicating the value of said throughput monitoring signal.
 4. Apparatus according to claim 3 wherein said conveyor belt means is arranged to convey said crop and unwanted material over an end roller of said conveyor belt means, and said conveyor belt means is so positioned that said crop and unwanted material passing over said end roller falls between said radiation source and said array of detecting devices.
 5. Apparatus according to claim 3 wherein said source of ionizing radiation generates periodic pulses of radiation and said detecting devices provide output signals in the form of pulses corresponding to the pulses of radiation received, and said second signal-level analyzer means includes counter means arranged to sum all output pulses from said detecting devices which have diminished magnitudes due to radiation attenuation.
 6. Apparatus for separating an agricultural crop from stones, clods and other unwanted material, comprising: harvesting means for harvesting the crop at a variable rate of harvesting; control means for controlling the rate of harvesting of said harvesting means; a source of ionizing radiation arranged to produce a laterally spread beam or array of beams of radiation; an array of radiation detecting devices positioned to receive radiation from said source; conveyor belt means for passing said crop and unwanted material in a laterally spread formation between said radiation source and said array of detecting devices; first signal-level analyzer means adapted to analyze the output signal levels of said detecting devices for distinguishing the crop from the unwanted material in dependence upon the degree of attenuation of said ionizing radiation by the crop and the unwanted material; an array of deflecting devices adapted to pass the crop and the unwanted material in different directions under the control of said first analyzer means; and second signal-level analyzer means connected to the outputs of said detecting devices for producing a throughput monitoring signal by combining the signal responses of said detecting devices resulting from attenuation of radiation by both crop and unwanted material, the output of said second analyzer means being connected to said control means of said harvesting means to control the rate of harvesting in dependence upon saId throughput monitoring signal.
 7. Apparatus according to claim 6 wherein said conveyor belt means is arranged to convey said crop and unwanted material over an end roller of said conveyor belt means, and said conveyor belt means is so positioned that said crop and unwanted material passing over said end roller falls between said radiation source and said array of detecting devices.
 8. Apparatus according to claim 7 wherein said deflecting devices comprise a plurality of fingers upon which said crop and unwanted material fall after passing through said radiation, each finger being controlled by at least one corresponding detecting device aligned with said finger in relation to the path of fall of said crop and unwanted material, each detecting device being arranged to differentiate between the crop and unwanted material as the mixture passes that detecting device, and said corresponding finger being actuated to pass the crop or unwanted material in the appropriate direction under the control of said associated detecting device or devices.
 9. Apparatus according to claim 6 wherein said source of ionizing radiation generates periodic pulses of radiation and said detecting devices provide output signals in the form of pulses corresponding to the pulses of radiation received, and said second signal-level analyzer means includes counter means arranged to sum all output pulses from said detecting devices which have diminished magnitudes due to radiation attenuation.
 10. Apparatus according to claim 9 in which said second signal-level analyzer means includes a reference generator means for generating a reference count corresponding to an optimum harvesting rate, and a reference comparator connected to compare said reference count with the output of said counter means, the output of said reference comparator being connected to feed a difference signal to said control means whereby the rate of harvesting is increased or decreased according to the sense and magnitude of the difference signal.
 11. Apparatus according to claim 6 wherein said control means comprises means for varying the ground speed of said harvesting means. 